Since the cost of servicing a luminaire such as a single street light can cost $100 or more on busy roads, and in busy areas, and since there are 60,000,000 street lights in the United States alone, the problem of high pressure sodium (HPS) street lights cycling at the end of their useful life is severe. The phenomena of cycling of HPS lamps as they age from use is caused by some of the electrode material being plated off the electrodes and then being deposited on the inside of the arc tube. This makes the tube darken and traps more heat inside the arc tube. As a result, an increased voltage is required to keep the lamp ignited or ionized. When the voltage limit of the ballast is reached, the lamp extinguishes by ceasing to ionize. Then, the lamp must cool down for several minutes before an attempt at re-ignition can be made. The result is "cycling" wherein the worn out lamp keeps trying to stay lighted. The voltage limit is reached, the lamp extinguishes, and then after an approximately one-two minute cool down period, the arc tube re-ignites and the light output increases again and until the voltage limit is reached whereupon the lamp again extinguishes. This repetitive on/off cycle is called cycling.
Cycling may waste electricity, cause RFI (radio frequency interference) which adversely effects communication circuits, radios, and televisions in the area, and may adversely effect and prematurely wear out the ballast, starter, and photocontroller.
For example, if an HPS lamp undergoes cycling for a few nights before it is finally serviced and replaced, the ballast or starter can be damaged or degraded. But, when the HPS lamp is replaced, this damage or degradation might not be detected. Later service calls then must be made to service these problems. The ballast and starter components are more expensive than the lamp or the photocontroller.
The cycling problem is well documented but so far the only solutions offered are to replace the HPS lamps with less efficient mercury lamps or to reconfigure existing photocontrollers with a special fiber optic sensor which senses light from the lamp and sends a signal to a microprocessor to indicate whether the lamp is on or off. After three on/off cycles, the microprocessor turns the lamp off and turns on a red strobe light which can be seen from the street. Unfortunately, this prior art solution requires modifications to the existing light fixture (e.g. a hole must be drilled in the fixture housing) and the use of an expensive fiber optic sensor.
Another problem with all luminaires including HPS or other types of lamps is the cost involved in correcting the cycling problem and other faults such as a lamp out condition. For example, a resident may report a lamp out or a cycling condition but when the repair personnel arrives several hours later, the lamp may have cycled back on. Considering the fact that the lamp pole may be 25-35 ft. high, repair personnel can waste a considerable amount of time checking each lamp in the area. Also, repair and maintenance personnel may not be able to service a given residential area until daylight hours when all of the street lights are off by design.